In aircraft actuation systems it has been conventional to employ some type of no-back apparatus to prevent aerodynamic loads from moving flight surfaces due to loss of torque reaction in case of failure of the drive train.
Historically two basic kinds of no-back apparatus are employed. They are the friction type and the ratchet type. Both of these no-back apparatus have advantages as well as inherent limitations. The friction type is quite reliable but tends to be relatively large, heavy and generally inefficient. The ratchet type no-back apparatus is compact and lightweight, but has been limited to applications with low inertia and rotational speed, because there is no inherent ability to dissipate energy.
It should, of course, be recognized that there have been mechanical movements that have been designed to permit power to be delivered into a shaft in either direction of rotation and to prevent such rotation when power is not so being delivered. These mechanical movements find utility in such environments as automobiles where they are incorporated in the power line shaft and adapted to act as an automatic brake which is rendered operative when the engine is retarding the automobile and inoperative when the engine is propelling the automobile.
The Mullan et al U.S. Pat. No. 1,833,224 ('224) illustrates a mechanical movement that is representative of this just mentioned type of arrangement. The '224 patent teaches the use of a differentially actuated brake which operates as a consequence of a driving shaft 10 having a threaded end portion cooperating with a nut 12 which is secured for rotation with a driven shaft 11. Friction brakes are secured to the nut 12 and depending upon the relative motion between the driving shaft 10 and the drive shaft 11, move the nut 12 and associated friction brake into and out of engagement. The '224 patent also provides for releasable bidirectional locking members 28 and 33 in the form of dogs. The '224 patent does not provide for backdriving relief in the form of energy absorbing frictional slip between the locking members 28, 33 and a fixed support as is provided in the invention to be described hereinafter.
The Rosin U.S. Pat. No. 2,240,043 ('043) is directed to an energy absorbing no-back drive mechanism suitable for use in an aircraft flap actuator drive for transmitting torque from one shaft to another which employs a load responsive clutch and a unidirection or no-back locking mechanism to minimize oscilation and chatter from the feed back torque of a load. The '043 patent does not teach the idea of having the no-back locking mechanism frictionally coupled to a housing to prove for energy absorption between the no-back locking mechanism and the housing as contemplated in the invention to be described hereinafter.
The Geppert U.S. Pat. No. 3,976,172 ('172) is directed to a ratchet no-back brake which allows essentially no obstruction to powered movement of the drive member in either direction. The '172 patent is a fair example of a ratchet no-back that is devoid of any energy absorption mechanism for the no-back brake as will be seen to be present in the subject invention to be described.